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Is there a simple relationship between angle of attack and lift coefficient?
Is there an equation relating AoA to lift coefficient?
I have been searching for a while: there are plenty of discussions about the relation between AoA and Lift, but few of them give an equation relating them.
I know that for small AoA, the relation is linear, but is there an equation that can model the relation accurately for large AoA as well? (so that we can see at what AoA stall occurs)
I am not looking for a very complicated equation. Can anyone just give me a simple model that is easy to understand?
(Of course, if it has to be complicated, then please give me a complicated equation)

Are you asking about a 2D airfoil or a full 3D wing?

@MikeY 3D is good, but 2D is OK

For a 3D wing, you can tailor the chord distribution, sweep, dihedral, twist, wing airfoil selection, and other parameters to get any number of different behaviors of lift versus angle of attack. So your question is just too general.

In the post-stall regime, airflow around the wing can be modelled as an elastic collision with the wing's lower surface, like a tennis ball striking a flat plate at an angle. Lift and drag are thus:
$$c_L = sin(2\alpha)$$
$$c_D = 1-cos(2\alpha)$$
I superimposed those (blue line) with measured data for a symmetric NACA-0015 airfoil and it matches fairly well. I don't know how well it works for cambered airfoils.

A bit late, but building on top of what Rainer P. commented above I approached the shape with a piecewise-defined function. Not perfect, but a good approximation for simple use cases.
$$
C_L =
\left\{
\begin{align*}
\sin(6 \alpha) ,\ \alpha &\in \left\{0\ <\ \alpha\ <\ \frac{\pi}{8},\ \frac{7\pi}{8}\ <\ \alpha\ <\ \pi\right\} \\
\sin\left(2\alpha\right) ,\ \alpha &\in \left\{\ \frac{\pi}{8}\le\ \alpha\ \le\frac{7\pi}{8}\right\}
\end{align*}
\right.
$$
Note that I'm using radians to avoid messing the formula with many fractional numbers. The post-stall regime starts at 15 degrees ($\pi/12$).

No, there's no simple equation for the relationship.
Here's an example lift coefficient graph:

(Image taken from http://www.aerospaceweb.org/question/airfoils/q0150b.shtml.)
This is actually three graphs overlaid on top of each other, for three different Reynolds numbers. I'll describe the graph for a Reynolds number of 360,000.
We see that the coefficient is 0 for an angle of attack of 0, then increases to about 1.05 at about 13 degrees (the stall angle of attack). From here, it quickly decreases to about 0.62 at about 16 degrees. Then it decreases slowly to 0.6 at 20 degrees, then increases slowly to 1.04 at 45 degrees, then all the way down to -0.97 at 140, then...
Well, in short, the behavior is pretty complex. The most accurate and easy-to-understand model is the graph itself.

"there's no simple equation". Could you give me a complicated equation to model it?

You could take the graph and do an interpolating fit to use in your code.

@Holding Arthur, the relationship of AOA and Coefficient of Lift is generally linear up to stall.  So for an air craft wing you are using the range of 0 to about 13 degrees (the stall angle of attack) for normal flight.  There is an interesting second maxima at 45 degrees, but here drag is off the charts.  This is why coefficient of lift and drag graphs are frequently published together,

@HoldingArthur Perhaps. What are you planning to use the equation for? I don't want to give you an equation that turns out to be useless for what you're planning to use it for.

Great graph and source (there's also a graph for drag), but the conclusion seems wrong. Based on those graphs, lift is clearly proportional to sin(2α) in the post-stall region.

@RainerP. But sin(2α) is only a useful model beyond about 35 degrees (before that, a linear model in the post-stall region works just fine). How much time do aircraft spend at such angles of attack?

The lift coefficient is linear under the potential flow assumptions. So just a linear equation can be used where potential flow is reasonable.
Potential flow solvers like XFoil can be used to calculate it for a given 2D section.
Or for 3D wings, lifting-line, vortex-lattice or vortex panel methods can be used (e.g. using XFLR5).
When the potential flow assumptions are not valid, more capable solvers are required.
XFoil has a very good boundary layer solver, which you can use to fit your "simple" model to (e.g. a spline approximation).
And I believe XFLR5 has a non-linear lifting line solver based on XFoil results.
For 3D wings, you'll need to figure out which methods apply to your flow conditions.
Possible candidates are: experimental data, non-linear lifting line, vortex panel methods with boundary layer solver, steady/unsteady RANS solvers, ...

You mention wanting a simple model that is easy to understand.  Always a noble goal.  You then relax your request to allow a complicated equation to model it.
@ruben3d suggests one fairly simple approach that can recover behavior to some extent.  However one could argue that it does not 'model' anything.
I.e. the arbitrary functions drawn that happen to resemble the observed behavior do not have any explanatory value.  You wanted something simple to understand -- @ruben3d's model does not advance understanding.
@ranier-p's approach uses a Newtonian flow model to explain behavior across a wide range of fully separated angle of attack.  That does a lot to advance understanding.
For most aircraft use, we are most interested in the well behaved attached potential flow region (say +-8 deg or so).  Much study and theory have gone into understanding what happens here.  Another ASE question also asks for an equation for lift.
Is there a formula for calculating lift coefficient based on the NACA airfoil?
In this limited range, we can have complex equations (that lead to a simple linear model).  These are based on formal derivations from the appropriate physics and math (thin airfoil theory).  They are complicated and difficult to understand -- but if you eventually understand them, they have much more value than an arbitrary curve that happens to lie near some observations.
On the other hand, using computational fluid dynamics (CFD), engineers can model the entire curve with relatively good confidence.
From one perspective, CFD is very simple -- we solve the conservation of mass, momentum, and energy (along with an equation of state) for a control volume surrounding the airfoil.  We divide that volume into many smaller volumes (or elements, or points) and then we solve the conservation equations on each tiny part -- until the whole thing converges.  I.e. we subject the problem to a great deal computational brute force.
This is a very powerful technique capable of modeling very complex flows -- and the fundamental equations and approach are pretty simple -- but it doesn't always provide very satisfying understanding because we lose a lot of transparency in the computational brute force.
I.e. It could be argued that that the Navier Stokes equations are the simple equations that answer your question.  But that probably isn't the answer you are looking for.
There is no simple answer to your question.  Instead, there is the fascinating field of aerodynamics.

Ehm, the asker would like to see "an equation relating AoA to lift coefficient", I don't see any in your answer...

@sophit that is because there is no such thing.  I try to make the point that just because you can draw a curve to match observation, you do not advance understanding unless that model is based on the physics.  I also try to make the point that just because a simple equation is not possible does not mean that it is impossible to understand or calculate.


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FAA Knowledge Test Question Bank - What is the source of the actual test questions?
According to various online search results, the FAA test questions are not made  available to the public (page 6), but used to be.  Yet, question books claim to have the exact real questions.
How are the latest questions obtained?  I am aware of the sample questions the FAA provides, yet publications and online study sites claim to have "the most up to date" actual questions.
Are the questions available by FOI request?  Does the FAA provide the questions to publishers on some limited basis?

I think some of the questions and answers are gathered or updated by crowdsourcing.

I think so too, and I suspect there is a bounty offered.  It would interesting to  know for sure.

I have studied using a program that encourages users to call in with new or updated questions, etc. There is no bounty offered that I am aware of, just the assurance that everyone appreciates the help.

I just took the Instrument Test and at least 90% of the questions were from old tests. There were a few that were very similar to the old test questions, just different numbers. I think that out of 60 questions there were 2 that I hadn’t seen before.

Years ago (35?), I taught ground school for pilots.  The question pool was not published then (it was later published, and then withdrawn), the company would send college students to take the FAA test, with the idea that they would capture certain questions, so that they could be edited and put into study guides.
As I recall the goal was about 5 questions per student taking a test.  Most of the students were not pilot candidates, but rather engineering and even humanities students at colleges.
Attendees would also report on small differences after they had taken the written, and the company question pool would be revised.
I cannot tell you what process is used today.

Interesting, indeed.  Apparently the FAA was offended by that.  The link I just added to the questions says, In some cases, unscrupulous test preparation providers have sought to obtain actual test questions by overtly or otherwise encouraging knowledge test takers to share information about actual questions and possible answers immediately after taking the knowledge test.  The FAA has taken action against such companies.

Interesting, I had not heard that, but then again I have not worked for that company for decades.  I can say that the FAA was aware of our question books, and actually sent employees to our courses. The company still provides training.

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sort: votes


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Has the FAA moved to change its use of gender-specific words like airman?
Last year, the United States Navy was ordered to review all of its job titles related to gender reference, e.g. yeoman, fireman and seaman.  The Air Force has initiatives to fully integrate women in all jobs, and has also been pressured to review job names: Air Force Times Story, Jan 14, 2016
Has the FAA taken any action to review or change gender-specific titles like "airman"?  Is there a non-gender specific title like "airperson" coming into use?  Terms like stewardess and cockpit have been dropped from parlance.
Is there anything official or brewing at the FAA on this subject?
I'd be interested in your comments if using flight crewmember would be a valid substitute for the term airman.

Onte thing they have done relatively recently is rename the Airman’s Information Manual to Aeronautical Information Manual. Many of the FAA publications now use 'he or she' instead of 'he'. I don’t know if there is a policy for that.

I don't see any need for this. "Man" is short-from for Man and "Man" is also short-form for "woman".

What was wrong with cockpit? Will it become henpit?

@JScarry Indeed there was a reason behind it.  It would be interesting to hear from an FAA insider.  I presume there is encouraged language that I have not yet seen.

@Koyovis "Flight Deck".

@TayE, any chance you're a man? That's usually how this sort of discussion goes, for what it's worth.

@egid Fair enough.

This AC from 2009 lays out some regulations on it for part 21 regulations

j. Replace the masculine pronouns “he” and “his” with gender-neutral
  terms. The new rule uses plain language.

It looks like they also made a lot of changes to the medical code in 1996 that covers it as well.

Where appropriate, changes are made to eliminate gender-specific pronouns, to replace ‘‘applicant’’ with ‘‘person,’’ to use current
  position titles and addresses, to correct spelling and improve syntax,
  and to adjust section and paragraph references.

Reading more about this, is seems the Associated Press holds sway in changing norms, at least as far as journalists speak, according to one story regarding the term mailman, "quoth the 2013 edition: "letter carrier is the preferred term because many women hold this job."

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text:
What is the groundspeed history of an aviation of such as a Boeing plane?
I would like to see groundspeed data of civil aircraft for distances such as 300 miles. What could it look like for a popular model such as Boeing 737?

This is wildly broad, ground speed is affected by many things, like wind. I'm not exactly sure what you are asking either, what do you mean "changes during a civil aviation"?

If you're looking for a plot of ground speed over a 300 mile flight, you can find this on flight tracking sites like FlightAware.

If what you're asking is to see groundspeed history of a certain type of aircraft, you can choose a type here:  aircraft type airborne now
Then follow the links to see its flight track history as shown here: Flight Aware Track History


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DIY switch panel
I'm looking to build a switch panel as a present for a friend who's found of flight simulation games.
The coding and interface to the computer is no issue, but I'm completely unaware of how an airplane is piloted, hence I have now idea which are the most used/important/common across all planes switchs that I should put on the panel.
To be complete, the panel should be composed of only buttons and switches, no potentio-meters and certainly not sim>hardware interfaces as those would involve too much money/time in the making.
My friend already possess a joystick and a gas thing (like to control the engine rpm I guess ?).
Thanks to anyone that can enlighten me =)
EDIT (on-hold status) :
I know how this will end but let's try at least. Can someone explicitly tell me how I'm off-topic ? To use the words from the very help page, I think my question is quite on point for aviation enthusiasts willing to know what instruments in a cockpit are important besides the stick/yoke and throttles. Moreover this doesn't fall into the explicit list of off-topics. I already got the answer I was looking for, so you can delete this post as you wish, potentially denying other people knowledge. Here is, for example, a guy asking about a painting process on panels. This is useful information.

Start with the basics and make "unrealistic" but practical panels at first. As your skills improve, along with your familiarity, you can advance to more realistic and/or complicated panels. I'd start off by basically copying these: http://www.saitek.com/uk/prod/switch.html , http://www.saitek.com/uk/prod/radio.html , http://www.saitek.com/uk/prod/multi.html

@SnakeDoc Alright mate, thanks for the quick reply. Looks like the first panel (switch) would be the easiest to make. I understand all of these are switches except the off/r/l/both/start and the gear up/down : are those behaving like discrete positions or more like a potentiometer (ie : does it mean something to be halfway between say "OFF" and "R", same for the gear thing )

For the engine starter (the off/r/l/both/start) switch, it's usually a multi-position rotary switch. You only need 5 positions, so you can just ignore (or not wire) the positions you aren't needing. To "feel" more authentic, it should probably click into position (so that the user knows it moved... there's no such thing as sort-of-on for ignition systems). Regarding the landing gear, you can get by with a simple toggle switch here. Gear is either down or up. I'd suggest taking a "joy" ride through the simulator, paying attention to what switches what, and when etc :)

Aircraft bone yards often sell parts like this for simulator use. You can get the real thing if you look around.

@SnakeDoc Wow thanks for the feedback mate, I think I'll have the gear up/down as a simple switch, maybe I'll go fancy and buy one of those switch with a covering red cap on top lol. As for the ignition system knob, this one might be tricky to find but I'll try.

@Dave Wow that guy ain't messing around with a whole plane head in his garage lol ! I like my buddy but not to that point I'm afraid =)

Rotary switches are easy enough to some by. Getting a switch cover that you like might be another story ;-P Here's one for example: https://www.amazon.com/Plastic-Position-Channel-Rotary-Switch/dp/B00DUYQJWQ

Good luck. Sim'ing is a lot of fun, and making your own gear is even more-so!

Alright guys, thanks for the feedback, to my surprise I found cheap 5 position rotary switches quite easily so that's good.
I'll post final product here once I get all the parts, cheers =)

One final question though, in flight simulators (I think my friend use flight simulator 10 but not sure) is a switch, let say beacon on/off, bound to a single toogle key ? Like do you bind say 'J' for 'toogle beacon on/off' or do you have to bind say 'J' : Beacon ON and 'K' : Beacon OFF ? I'm asking this because I'm pre-coding most of it so once I get the parts it's already ready to go =)

In FSX, most of the keys act ON/OFF (e.g. G for gear UP/DOWN)/ Some are used differently, e.g. flaps retract/extend (F6/F7). But anyway everything can be customized. See default key bindings

About your edit, as you can see I have not voted, but I understand those who did. Also, only 3 of the voters selected it, the other two probably voted as "too broad". The problem here is that you are not giving us any kind of technical detail, and an answer should cover all possible aspects of all possible combinations of switches you might need. As for the "aviation enthusiast" side of your point, we refer generally to people interested to the elements of aviation, and hobby-ism (including RC and simulators) has not generally being considered within our scope.

Adding to Federico, the problem is the scope is not limited (too broad) and actually seems to change when additional knowledge is provided, ending in the discussion format which the stack is not for. This is enough to trigger the closure (as you see I didn't either vote to close, but I could have). While you triggered interest, it could be more convenient to use the chat format. Why not try to start a room for this topic?

Alright I'd like to thank Federico and mins for at least giving me explicit reasons. I disagree with what you said as for me, asking "what are the essential switchs a cockpit should have" doesn't seem to be too broad or subject to change. Indeed in the comments I allowed myself to add another question about sim key binding but I do think that's what comments are for. Again, I might be wrong, I come from Math stack where trust me people are absolutely strict about off topic, but maybe I'm missing subtleties specific to Aviation stack. Still, thanks to both of you.

As mins said, I encourage you to pass by chat, we could work on a way to save the question :)

Since you want further clarification on why explaining the essential switches is "too broad", take a look at all the differences in these cockpits.  Explaining the differences would take a very lengthy discussion of avionics: http://aviationbookreviews.com/wp-content/uploads/2012/09/glider-cockpit-2.jpg http://www.cap-ny153.org/Cockpit%20Cessna%20C172%20Instrument%20Panel.jpg http://www.twomoreweeks.net/wp-content/uploads/2016/05/F-16-Cockpit-2.jpg http://www.gulfstream.com/assets/images/_500/img19-zoom.jpg


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What do the white dumb-bell signals indicate?
From ICAO Annex 2:

4.2.3.1 A horizontal white dumb-bell (Figure A1-4) when displayed in a signal area indicates that aircraft are required to land, take off and taxi on runways and taxiways only.

4.2.3.2 The same horizontal white dumb-bell as in 4.2.3.1 but with a black bar placed perpendicular to the shaft across each circular portion of the dumb-bell (Figure A1-5) when displayed in a signal area indicates that aircraft are required to land and take off on runways only, but other manoeuvres need not be confined to runways and taxiways.

The text from Annex 2 is clear. For the first one, aircraft are required to land, take off and taxi on runways and taxiways only. But when is this not the case? Why would you need a signal to specify this - isn't it normally the case that you need to land, take off and taxi on runways and taxiways? Same question for the second one, basically.
Please try to elaborate on the text from Annex 2, and give examples of practical use of these two signals.

One possibility is if you are allowed to taxi through the grass...

One example would be Thruxton in the UK where I learned to fly helicopters. We would take off, land and taxi pretty much where we wanted, giving way to the planks of course ;)

These symbols are intended for old-fashioned "airfields" which just have a large grass area instead of a runway. This used to be the norm before the increasing weight of aircraft in the Second World War. The whole surface of such a site is suitable for the movement of aircraft, so you don't need to be on a particular runway or taxiway: you can just take-off and land in the wind direction.
This was the norm when the ICAO rules were drawn up, so the case of only being allowed to operate on a particular surface was the exception then, not the rule. The runway-only aerodromes probably wouldn't have their grass in good condition, so it would be dangerous to land on grass: you might put your undercarriage in a rabbit hole. Back then, when most aircraft didn't have radio, you would have needed a signal at the unusual runway-only aerodromes so that visiting pilots wouldn't assume it was OK to land where they liked. The signal would more likely be a permanent fixture at these aerodromes, rather than something flown at particular times.
Nowadays, the only situation where this is common is in glider flying. At a popular glider site, there might be a hard runway provided for the tow airplane or for winch launches, but gliders can land anywhere on the aerodrome. Or there might be a marked (hard or grass) runway for take-off and landing, but no taxiways at all: you just vacate onto the grass. As Jay Carr points out, a fly-in or a gliding competition would be an example of when a particular aerodrome might change from one to the other, but that might go either way. The same aerodrome where normally everyone lands on grass might be worried about the condition of the grass at a high-traffic event (and about the safety implications of a variable landing direction), so they might have people stick to the runway for that one event.

Hi, both signals are normally used in a no controlled airdrome, the ones which has no radios aircraft operating.  It will indicate to the pilots there are parts of the movement area unserviceable, can be due to softness or wet, most probably in grass fields.  In case of hard surface, indicates to stay in the runway or taxiways, do not taxi or park the aircraft outside of the hard surfaces.Both signals are time-limited due to weather.  This kind of signal must be used with careful in  airport that have more than one runway, it can be dangerous to identify the correct RWY.

I keep thinking of some of the big fly ins (like Air Venture in Oshkosh) where pilots are allowed to park on the grass.
During the fly in they might use that second symbol (dumbbell with stripes) to let people know it's okay to park on the grass, but you still need to take off, land, and taxi on official taxiways and runways (as defined by the event rules).  Thus significantly increasing capacity during the event.
But during other weeks that same airport probably doesn't want anyone taxing onto, or parking on, the grass.  So they would display the first symbol (dumbbell with no stripes) to remind everyone that the exception is gone, and the rules have changed back to what you would normally expect at most airports.  Thus people would be aware they need to stay off the grass and use official tie down areas for parking.
In essence, I think the first symbol exists mostly because of the second one.  At airports where there are occasionally exceptions along the lines of those described above, they may also want a symbol to help pilots know when the exceptions are not in effect.

Thanks for your answer - I appreciate it. While you do present a reasonable explanation, I was hoping for an answer from someone with practical experience and/or appropriate sources. It sounds like your answer is mostly an educated guess. If this is not the case, please feel free to update the phrasing to reflect that.

@J.Hougaard It's just an educated guess, though I did my best to display the logic I'm using.  If it makes you feel any better, I've been patiently waiting for someone with actual experience to show up and explain it to, just to check my logic, ya know?  You might try posting a link to this question on www.redddit.com/r/flying to see if you can draw someone in who might know.

@J.Hougaard In fact I felt so strongly about it, I put it on r/flying myself.  Hopefully it draws someone in...

Great, let's hope so! :)


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What would happen if a Cessna flew into a power line?
When I was going through my private pilot training, I asked my instructor what would happen if a Cessna flew into a power line. His response was that the power line would go through the single engine plane like a cheese slicer, no challenge.
How accurate is this statement? I - luckily - haven't come across any evidence to support one way or another.

It would depend on what kind of line you hit. If you hit a high tension line (the ones on the big towers), you would probably crumple it up. If you hit one of the lower voltage lines on the poles, it would probably snap after going into the wing or ripping the gear off. Either way it would very much ruin your day, the result is pretty much the same, a balled up airplane. There are a few YouTube videos you can watch that I won't copy here.

The power line wins every time. At my home airfield an airplane was scud running into 22L and went under a high tension pylon, sliced the top of the tail clean off. The idiot fortunately managed to land safely, if he'd been flying 3 inches higher it would have been a different story.

GdD -- sadly, there are people who pull that scud running sh*t here, too. Do you think the powerline would've acted the same once it hit the cockpit glass?

There are a lot of variables so its hard to make a flat out call. Here is at least one example of it happening that was caught on film. In that instance it seems to have ripped through the cords (which also appears to have started a fire). However here is an example of a similar situation where the plane simply got tangled into the cables and hung there. This one from my home field (ill go do some more digging) but it looks like the cable ripped it apart.
I would say you have a few mitigating factors,

Is the engine running? the prop is sure to do some slicing on impact if your engine is running and your prop is turning.
The cable type. As Ron mentions in the comments the type of cable will have an effect on this. The higher voltage cables tend to be solid twisted cable securely affixed to the larger towers. While the stuff out side your house is of a much smaller gauge and possibly is a phone line or other coax line etc.
Speed and size. There are lots of aircrafts that are all capable of very different types of flights. A Mooney Mite on departure is going to impact a power line in a far different manner than a King Air on departure. Its simply a matter of inertia.
Insulation Joints. Power lines are generally connected to towers via some kind of insulated connector. Often times the connectors used can break away under enough force allowing the line to drop to the ground. This of course depends on the type of connection joint and direction of force applied.


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What priority if any is given to Emergency Services in flight clearance?
When requesting takeoff/landing and route clearance is any priority given to Emergency Services IE air ambulances, firefighting rigs, S&R etc. I'm assuming even though these services rise to the level of life or death, they are not treated with the same urgency as an air emergency but I don't know that for fact.

They are not treated as an in-flight emergency, but they are given priority handling by ATC. Usually this means that they will not reroute the flight around traffic and hold other traffic to give them an earlier landing spot or get them into the pattern ahead of other aircraft. I don't know what regulations there are though for handling these flights.

I work as a fixed-wing pilot for a hospital-based Air Ambulance program. Let me add my experience to the ATC orders accurately cited by Pondlife's answer: the MEDEVAC call sign (the old "Lifeguard" is still used when filing the flight plan) indicates a need for priority handling.
ATC is often helpful in providing us with priority routing. This includes giving us direct clearances, moving us up in the landing que, allowing us an unrestricted approach speed, and otherwise expediting our flight. However, ATC does not always provide priority handling, and I have often experienced ground delays of 5-10+ minutes as ATC apparently prioritizes other traffic, including air cargo and the like. This is rarely a big problem as patients are typically stable, but it can be frustrating when priority handling is expected.
However, if medical staff determine that a patient is in critical condition, we will announce this to ATC—typically accompanied by a request for a specific clearance or change to a previous clearance. This announcement re-iterates our need for priority handling and indicates the urgency of the situation. In this way we can work with ATC to best care for the patient. We will often make such an announcement when checking on with approach control for their information with no specific accompanying request. Occasionally, however, we will need to request such priority handling because ATC has issued us speed restrictions or delaying vectors to put us behind other traffic. ATC is very good at working with us when we do need the priority handling.
In other words, ATC usually automatically gives us priority handling, but when they don't—and we need it—we ask for it and they are very good at working with us to provide the priority handling.

can imagine why a large cargo aircraft would get priority over a non-critical medical flight. A 5 minute delay on getting it out of its parking spot can cause more delays along the line as someone else may already be waiting to park there, causing queues on the taxiways.

@jwenting These are usually small feeder cargo aircraft that I have in mind.

Apologies for this naive question, but do airplanes not declare Pan-pan (urgency) if they have a seriously-ill passenger?

@ChrisW Declaring pan-pan would be an option for communicating an urgency situation. However, that option seems best reserved for use in situations outside of our normal sphere of operations, but would certainly be appropriate for a non-medevac flight to use in the case of medical emergency. More importantly for us, our ops manual does not direct us to use that phraseology.

@ChrisW Pan-Pan (or even Mayday) is more likely to be used by non-emergency-services flights (i.e. normal airline flights, normal GA flights, etc.) when there's a medical emergency. It's kind of assumed that a Medevac flight has a medical emergency... otherwise they wouldn't be using the callsign "Medevac" in the first place.

So a Medevac flight with a patient on-board is given priority handling when possible, but is not, itself, an emergent flight. A Medevac flight, where a crew member has an emergency as well, might. Right?

@CGCampbell Yes, that is correct. But it is worth noting that a patient need not be aboard to warrant the callsign and accompanying urgency. The callsign is also for use whilst enroute to pick up a patient. I do not, however, use the callsign on an empty return flight after dropping off a patient.

@CGCampbell, note that even regular flights when a passenger becomes ill usually don't declare “emergency” but there is a separate “medical emergency” for the purpose. Because such flights, and medevac ones, need priority, but don't need any other special handling that is normally associated with emergency. Full emergency is normally only used when pilot becomes ill, because then it affects ability of the remaining pilot to handle the plane due to the increased workload.

In my experience, yes they will hold for emergency related vehicles. I fly out of KPNE often, where a lot of the Philly Police and Emergency choppers are kept. I have been held for their takeoff before. I don't know if this is regulation or simple courtesy but I can assure you it happens.
On a similar note, I once spoke to the designer of the Philly Bravo airspace about this very issue. He explained that when the airspace was redesigned (a few decades ago now) the shelves were deliberately placed so that all of the hospital helipads were accessible without entering the bravo. Basically the emergency choppers can come and go with out clogging ATC for clearance in and out of the Bravo.
In uncontrolled airspace this is not really an issue and emergency helicopters will rarely go into class A. So this leaves you with Class B, C and D departures and arrivals. In the case of Philly the helicopters are stored at a less busy airport outside of the bravo for operations commonly under the shelf. This most likely varies heavily from place to place and their may be arranged understandings in different Bravo's.

(I'm assuming you're asking about the US, based on your profile.)
The FAA's ATC orders section 2-1-4 has a list of aircraft operations that should be given priority, including emergency service flights, but an aircraft in distress always has the highest priority:

Provide air traffic control service to aircraft on a “first
  come, first served” basis as circumstances permit,
  except the following:
[...]
a. An aircraft in distress has the right of way over
  all other air traffic
[...]
b. Provide priority to civilian air ambulance flights (call sign
  “MEDEVAC”). Use of the MEDEVAC call sign indicates that operational
  priority is requested. When verbally requested, provide priority to
  AIR EVAC, HOSP, and scheduled air carrier/air taxi flights. Assist the
  pilots of MEDEVAC, AIR EVAC, and HOSP aircraft to avoid areas of
  significant weather and turbulent conditions. When requested by a
  pilot, provide notifications to expedite ground handling of patients,
  vital organs, or urgently needed medical materials.

Other flights that get priority are presidential ones, search and rescue etc.

presidential flights would likely lead to a temporaty NOTAM and closed airspace around the time of arrival and departure (and in extreme cases presence), the ultimate priority clearance as he'd be the only aircraft in the pattern :)

@jwenting Yeah, when I read this I was thinking 'priority' is quite the understatement to describe handling of Presidential transport flights. They get a TFR to mostly shut down the airspace and movement of everyone else on the field stops.

However, even under a 'Presidential TFR', a justified MEDEVAC flight can still fly, yes?

@CGCampbell I'd guess if it were critical enough, but they'd no doubt try to accommodate through other means (maybe get an air force gulfstream in with a military crew.

@CGCampbell If you look at the text of VIP TFRs, air ambulance flights  typically are or could be authorized. For example FDC 7/5997: medevac/air ambulance flights on active missions; or FDC 7/7287: approved air ambulance flights. [...] All emergency/life saving flight (medical/law enforcement/firefighting) operations must coordinate with ATC prior to their departure [...] to avoid potential delays.


text:
How long does AFSP processing take the second time?
If you've already completed the fingerprinting for the TSA's Alien Flight Student Program and been approved to train at one flight school, how long does it take to gain approval to fly at another flight school?

Hi @Zaz How long did it take for your first time? I'm waiting for their response as well :(

@newBike Jul-14 Fingerprinting instructions received.  Jul-26 Fingerprinted.  Jul-27 Permission to initiate training.  Jul-27 Final approval.

@Zaz How long did you wait for the fingerprinting email after you paid the $130 fee?

@arpurush: I received instructions to pay the fee on Jul-11, so I believe 3 days.

Assuming that you're a category 3 applicant, you can start training as soon as they confirm receipt of your completed application but there's no specific processing time. This is from the AFSP FAQ (direct links to FAQ items don't work):

Category 3 Candidates may commence training after receiving the "Permission to Initiate Training/Fingerprint Receipt" e-mail, which AFSP issues upon receiving all required information (including fingerprints and the fee).

There is a guaranteed processing time for categories 1 and 2 (aircraft greater than 12,500lbs MTOW), however:

In accordance with Section 612 of Vision 100 and the IFR, the AFSP conducts a threat assessment on Category 1 Candidates within 30 calendar days of receiving all of the required information, including fingerprints and the fee. The AFSP conducts a threat assessment on Category 2 Candidates within 5 business days of receiving all of the required information, including fingerprints and the fee.

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text:
Why are many runways used just for departures/arrivals?
At LAX and many other large airports they designate certain runways for landing or takeoffs Normally. Why is this? I think its inefficient use of available runways.

There are many constraints on runway usage, and sometimes it's not the runways themselves but the protected airspace for approaches that determines what "normal" is - as well as airport design, noise abatement, wind, aircraft type, taxiway configuration, departure routes in use, etc.  It is typically more efficient (= less delay) to run all of one type of operation on a runway: you can launch more departures faster if you're not trying to land other aircraft in between them, so if there is a major departure push on, the tower will try to dedicate at least one runway to departures only.  Same thing for arrivals: landing aircraft need to be spaced further apart if there are departures going out on the same runway, and if a departure can't roll as soon as expected (for example, if the last arrival doesn't clear the runway as quickly as possible), the next arrival may have to go around because the next departure is still sitting on the numbers.  Having said that, unless the airport management puts specific restrictions on runway usage, ATC is free to shuffle the deck any way they see fit and land/depart from any appropriate runway if operational needs require it.  Pilots also have the right to request a specific runway for THEIR operational needs, and ATC will accommodate the request even if it isn't exactly their current plan.
LAX generally lands on the outboard runways because the final approaches are further apart, and taxiing is less complex if the departures go off the inboard runways.  That doesn't mean they never do anything else, but that's kind of the "normal" case.

I believe it is not, actually, more efficient to use one runway for landings and one for take-offs. The separation between landings that allows to squeeze a take-off in is usually less than double the minimum, so interleaving on two runways should allow more operations in given time. Using one runway for landings and one for take-offs is, however, much easier to coordinate and therefore safer.

As usual, "it depends."  If arrival and departure demand are about equal so the finals are packed and a departure gets off between every arrival, the overall demand may be better met by running both runways in mixed mode - but that is a fairly unusual situation.  Due to the vagaries of airline hub operations, it's more common (at least in the US) to have imbalances in demand.  Depending on the mix of aircraft, the tower can bang out the next departure as fast at the preceding one breaks ground - and there is no room for an arrival in there.

For imbalanced load, optimal scheduling will almost always involve switching both in a rather ad-hoc fashion. However, it would be pretty hard—and thus prone to potentially fatal mistakes—to keep track of it. Using one runway for take-offs and one for landings has the big benefit of keeping things simple and regular.


text:
Why is Saturday a typical slow day for airlines? Not weekends, but Saturdays?
Why are Saturdays typically slower days for airlines? I have always heard that they are but never a reason why.

A good majority of passengers are business passengers, who don't really want to travel on their days off.

The airlines fly less when people want to fly less. Why do people want to fly less on Saturdays? That's probably better for Travel.SE. I'd say it's because business travellers make up a huge percentage of airline passengers and they don't need to fly on Saturdays. Sunday afternoons are usually busy as they get to where they need to be for Monday morning.

Saturday is indeed slow day. Sundays are full of people getting back from holidays, or before the working week. Mon-Fri are people travelling on business, or (for Friday) back home before weekend.

@RonBeyer: Wouldn't their days off be the only days when they'd have time available to fly?

@Sean No, because they want to be home on the weekends and do "work activities" during paid work days. So usually a business traveler will travel on Monday's (to the site) and Fridays (home) so that they have the weekend with their friends/families. I wouldn't want to travel home on Saturday and back out on Sunday, there would be no point...


text:
Do the ICAO and IATA codes for an airport ever change?
Do ICAO and IATA codes ever change for airports in time? If they do, how often does it occur? I am developing an app for airports and I am thinking of setting the uniqueness of an airport through ICAO or IATA codes.

The app you're developing, I'm assuming that you'll probably be using some sort of a database to get the ICAO codes. That said, the database admin will probably handle the updates.

This might be straying into software development, but whereas those codes might make good unique indexes they might not make good primary keys. You mention the former, but I worry you actually mean the latter

We're just a few months away from IST changing from LTBA to LTFM https://en.wikipedia.org/wiki/Istanbul_New_Airport

Yes it does happen.

A city can build a new airport, in which case it will usually get a new ICAO code, but will get the original IATA (city) code. For example, Oslo changed from Fornebu to Gardemoen - Fornebu is ENFB, Gardemoen is ENGM; the OSL code was Fornebu but uis now Gardemoen.
A city can rename its airport for political reasons, so again the codes are liable to change.
Example 1 is New York - Idlewild KIDL was change to John F Kennedy KJFK
Example 2 is Johannesburg - Jan Smuts International was FAJS, then renamed to Oliver Tambo International FAOR.

Yes.  It's a pretty big deal so it won't happen often.
Changing the major airport for a city is a big reason.  I think both Denver and Austin did this (new airport opened with a different code, then took over the old airport code).
Renames can also happen.  JFK used to be IDL.

Another example would be Hong Kong...

And Beijing, Bangkok, Istanbul…


text:
Does the Piper PA-28 Cherokee have a limitation on its maximum lifetime flight hours?
Is there a lifetime limit on the (airframe) flying hours of an aircraft (specifically the Piper Cherokee)?

Do you mean for a single flight, or during the lifetime of the airframe?

Until you run out of fuel.  Flying with tanks at 0G is not permitted.

"As it's currently written, it’s hard to tell exactly what you're asking." (voting to close)

I believe you're asking if there are a maximum number of airframe hours over the lifetime of the PA-28. Is that what you're after?

Pantelis - I edited the question to more directly ask what I think you were after.  If this isn't what you were after, please feel free to roll back my edit & clarify what it is you're asking.

Dear friends, i want to know if a Piper or in general an aircraft of general aviation has a time limit in flying hours (written by the manufacturer)

Possible duplicate of Is there any limit by FAA on the age of aircraft to be operational? It may not be an exact duplicate, but it's very close, IMO

Short answer, not in the United States; as long as the airframe is regularly maintained and passes its mechanical inspections, it can continue to fly. Some reasons this is so (when it might not be true for other models) include:

The Cherokee is non-pressurized. Pressurized aircraft are often rated for a lifetime limit of pressurization cycles (determined by the number of times the aircraft rises above and then descends below the altitude at which the pressurization system kicks in, typically 8000ft MSL for many small craft). This pressurization stresses the airframe in ways that eventually more or less requires the entire fuselage to be replaced in order for the airframe to pass its next mechanical as originally rated. The Cherokee, however, has no system for full-cabin pressurization and so its fuselage is not subjected to these stresses.
The Cherokee (180 or 235) is not rated for aerobatic maneuvers, and so does not typically perform them. Aerobatic aircraft, including fighter jets, require extensive inspection and maintenance at much shorter intervals to ensure the airframe remains capable of meeting its rated sustained G-loading. Coupled with regular testing of those ratings by the pilot, aerobatic aircraft are more quickly retired from service when it becomes impractical to repair or replace overstressed structural members.
The Cherokee is not commonly used in Part 121 or 135 operations involving passengers or air freight. As a four-seat single-engine, its capacity for passengers and cargo is limited, and so its usefulness to major airlines which are subject to Class D(econstruction) inspections every 6 years is sharply limited. Bush airlines like Era Alaska might see some use as more or less an air taxi, but even these outfits prefer somewhat larger planes for more flexibility and longer range.

Seems like a straightforward question to me.
No, the PA-28 has no published lifetime airframe limit.  Governing bodies may establish a life limit for their own countries but it will be a largely arbitrary number.


text:
If an aircraft cannot fly above 300ft, is it an aircraft?
I saw a question here that inspired one of my own. If an larger, person carrying aircraft, say some sort of hovercraft, could not fly above 300 ft would it be allowed to fly? Here in Australia, 300ft is the minimum height for an aircraft to fly over a town, so if an aircraft simply could not go any higher would it be allowed to fly at all? Or only in certain circumstances?

There are two different questions here, "is it an aircraft" (in your title) and "is it allowed to fly". It would most certainly be considered an aircraft regardless of altitude (debatable I guess, but if it supports its own weight in the air, I would consider it an aircraft). Is it allowed to fly is different and more complicated, depends on where you want to fly I guess, as long as you can meet minimum altitude requirements, it should be a "yes", but those requirements change depending on location...

Plz check this answer for the FAA definition of an aircraft: it does not state a maximum altitude. So according to the FAA it would be an aircraft, most probably according to CASA as well.

@RonBeyer, If you chuck this in as an answer, I'll accept it!

What sort of aircraft wouldn't be able to fly higher than 300 feet? I would think that any aircraft which can't go above 300 feet would also have a lot of trouble at 100 feet, since the difference in air pressure between 100 feet and 300 feet is pretty small.

related: https://en.wikipedia.org/wiki/Ground_effect_vehicle

Would a hovercraft even be considered an aircraft?  AFAIK they can manage only a few feet altitude, not 300.

There is actually a legal Australian definition for aircraft, in Part 1 section 3 of the Civil Aviation Act:

aircraft means any machine or craft that can derive support in the atmosphere from the reactions of the air, other than the reactions of the air against the earth’s surface.

So those drones you can buy from the store are aircraft (and if you knock one out of the sky because it annoys you, you are technically bringing down an aircraft and could be punished). However the latter half of that definition suggests hovercrafts are not aircraft.
Also, the minimum height over populated areas in Australia is 1000ft, and 500ft over non-populated areas (CAR157)

That is a funny definition because, strictly interpreted, it excludes all heavier than air aircraft. A hovercraft flies the same way as a helicopter or an aircraft, only that the pressure field on the ground is more limited and more visible.

@PeterKämpf That seems not correct. A hovercraft relies on the increased air pressure between ground, hull, and skirt. Take the ground (or the skirt) away, and the hovercraft will not hover any more.

@bogl: Every aircraft needs to accelerate air downwards in order to create lift. How is this acceleration stopped? By extra pressure on the ground. Only that you hardly notice that pressure increase because it is spread over such a wide area for a high flying aircraft. Now move it down to hovercraft altitude and the pressure increase is easily noticed - just as it is for a hovercraft. In principle, there is no defining difference. Take the ground away, and an aircraft will also not fly eventually.

@PeterKämpf Yeah, and without ground there wouldn't be plane factories and pilots anyway. But no - the notion of removing the ground is a theoretical one. Atmospheric pressure on a planet depends on the existence of a ground, yes, but aircraft lift does not immediately depend on a ground. Hovercraft and GEV directly rely on the proximity of ground.


text:
What is the maximum crosswind limit for a C150/2 aircraft?
What is the maximum crosswind limit for a C150 or C152 aircraft?
Does this change depending on the class of licence?
Are there exceptions for emergencies?

The POH lists the maximum demonstrated cross wind, but it does not state a limit. The limit is where the rudder runs out and does not change based on your license. You can do anything you want in an emergency required to meet that emergency.

Related but not quite the same and also related

Section 4  of the C152 POH lists the demonstrated crosswind component as 12KIAS. The 150 had a few variants so finding a published number is a bit more tricky. The Aerobat's are sometimes listed as 13KIAS, sometimes 15KIAS - but in general its the same sort of range as the 152(ish!).
You will only ever see "demonstrated" next to these numbers, it is not the maximum possible - I regularly hear of people landing 152's over that 12KIAS.
The number does not change due to your license privileges, it changes based on what the pilot is comfortable with /able to handle safely. Personally I would be wary of any crosswind over about 9/10KIAS.
In an emergency almost everything is an exception. Except aviate.

Not an answer, but too long for a comment.
A recent FAA email pointed out this interesting fact about what is commonly referred to as “Maximum Demonstrated Crosswind”. From the Airplane Flying Handbook p. 8-17.
Maximum Safe Crosswind Velocities
Before an airplane is type certificated by the Federal Aviation Administration (FAA), it must be flight tested to meet certain requirements. Among these is the demonstration of being satisfactorily controllable with no exceptional degree of skill or alertness on the part of the pilot in 90° crosswinds up to a velocity equal to 0.2 VSO. This means a windspeed of two-tenths of the airplane’s stalling speed with power off and landing gear/flaps down. Regulations require that the demonstrated crosswind velocity be included on a placard in airplanes certificated after May 3, 1962.
I’ve seen a lot of airplanes and I’ve never seen a placard indicating the demonstrated crosswind velocity. Probably because they were all certificated under CAR3 in the 1950s. The general rule of thumb I’ve used is that 10kts is no big deal, 15 kts is tricky.
Edited based on the comment by @Gerry
Using the information in the Airplane Flying Handbook, my old 182F has a VSO (flaps out 40°) of around 51 kts. So the Maximum Minimum  Demonstrated Crosswind is 10.2 kts.
My 210L has a VSO (landing gear down and flaps out 30°) of 51 kts. So the Maximum Minimum Demonstrated Crosswind is 11.3 kts.
My Cherokee 140 has a VSO (flaps out 30°) of around 48 kts. So the Maximum Minimum Demonstrated Crosswind is 9.6 kts.
None of these has a placard or data in the POH.

The numbers you've calculated are actually the minimum crosswind that's acceptable -- the Maximum Demonstrated Crosswind must be equal or greater than 0.2 * VSO.  In My C172P manual, it states that the VSO (bottom of white arc) is 33 KIAS.  That would imply a demonstrated crosswind must be at least 6.6 knots.  In Section 4 Normal Procedures, under Crosswind Landing it states: "Operations in direct crosswinds of 15 knots has been demonstrated."  So, in the case of the C172, the maximum demonstrated crosswind is 0.45 * VSO.

In flight training, I landed a Cessna 150 K in a 90 degree crosswind gusting to 55 knots. It was actually a smooth landing and when I settled her down, i was a foot off the centreline. I am not a wonder pilot by any stretch. The place I learned taught you to fly in the worst conditions, you came out of there as a bush pilot. You knew what you and the aircraft was able to do. Yes the crosswind chart had these conditions well off the edge of the page. The plane didn't seem to know it. I just crabbed her in slightly upwind looking out the side window mostly. The instructor said very little. he liked it.

Can confirm.  A 150 will handle extreme crosswinds with a little work from the pilot.  Just don't use flaps and don't stop flying it until you come to a stop!  I almost beat that dust storm back to town.

In theory, crosswind speed and direction is not the real issue when handling a crosswind landing in a C-150.  (Well, within reason.) Just point your nose into the wind and watch carefully to make sure you are tracking down the center line.  Everything will be perfectly fine right up to the moment that you actually want to land.  It is that split instant when rubber meets asphalt that is going to tell you how good a pilot you really are. And the higher the windspeed and the steeper the angle it is crossing the runway, the better you need to be.  And oh yes, pay attention to your aileron positioning. Don’t let the wind get under your upwind wing.  (I think I explained this right...)


text:
What are the FAA regulations on lighting for ultralight vehicles?
I'm in the process of scoping out a project involving an ultralight vehicle and some Neo pixel LEDs.
In the US, there are many regulations for lights on cars. Things like the location on the vehicle, the direction, color and blink rate are all regulated.
What lighting laws apply to ultralight vehicles, as far as location, direction, color and blink rate?

Hopefully you don't plan on flying at night since, in states other than Alaska, flying an ultralight at night is against the law.

@RonBeyer except 30 minutes before / after, and in G airspace

Ultralights are regulated under 14 CFR 103 and there are very few regulations of any kind that apply to them.
The only specific lighting requirement is in 103.11(b):

§103.11   Daylight operations.
(a) No person may operate an ultralight vehicle except between the
  hours of sunrise and sunset.
(b) Notwithstanding paragraph (a) of this section, ultralight vehicles
  may be operated during the twilight periods 30 minutes before official
  sunrise and 30 minutes after official sunset or, in Alaska, during the
  period of civil twilight as defined in the Air Almanac, if:
(1) The vehicle is equipped with an operating anticollision light
  visible for at least 3 statute miles; and
(2) All operations are conducted in uncontrolled airspace.

This question and this one have some information about what an anticollision light actually is (a beacon and/or strobe), but since ultralights are so lightly regulated I'd be surprised if anyone cares much about the exact form of lighting. However, you could check with your local EAA chapter or ultralight club to see what people typically use.


text:
Why do the CRJ700 window shades open in different directions?
On a CRJ700, the window shades in the rows immediately fore and aft of the exit doors open downward. All the rest open upward. Seen on more than one aircraft. Is there an engineering rationale for this?

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text:
When will I hear the sonic boom from a plane flying towards me?
When does a person first hear a plane, flying faster than the speed of sound, as it flies directly overhead? Yes, I know there is a sonic boom and I also know the plane will produce sound as it flies away from that person. But what about the sound that the plane produces as it's flying towards the person? Will the sound be different from the sound heard after the plane has passed?
My dad and I have discussed this and looked at a partial explanation on Youtube, but there wasn't anything - as far as we could find - on the sound produced when the plane was coming towards a person.

The sonic boom is like a wave created by the bow of a boat, it's a V shape following the aircraft. You'll hear it after the aircraft has passed, like the wave from the boat lands on the bank of a river after the boat has passed. The delay depending on the distance of the aircraft

A few seconds after it passes you.

In case a supersonic aircraft (flying faster than the speed of sound) flies directly over a person, that person (the observer) will not hear anything.
The (supersonic) aircraft produces sound throughout its flight (i.e. while flying towards as well as away from you).
The sonic boom you hear is the sound produced by the aircraft when it was coming towards you.
For how this works, see this question and the Wikipedia page.


text:
Where to find the LSA exporting requirements from the USA?
I'm planning to visit the US to buy an LSA (light sport aircraft) then export it to Saudi Arabia, I'm not a US citizen, where to find the requirements?

Buy it Then Export it :)

Export it where?

To Saudi Arabia


text:
Most time-consuming tasks while a plane is on the ground
How long should commercial planes stay on the ground after landing before they can take off again? What is the most time-consuming thing/task/operation that happens during this time? Is downloading maintenance data from a plane time-consuming?

Maintenance data are not downloaded during turn-around. The important bits are sent over the air (over the satellite; the system is called ACARS) in flight so the mechanics can have spare parts already at hand when the plane lands and then some more details may be printed from the system in cockpit, but that only takes a couple of seconds.

Commercial aircraft only make money while in the air, so they should be on the ground as little as possible. How long they are actually on the ground varies with size of aircraft, schedule demands and type of operator.
Transoceanic flights are typically scheduled twice per day for a given aircraft. Schedules are at fixed times and there is usually only enough time for two crossings. This leaves a lot of time to "turn" the aircraft, so the pace is very relaxed.
LCCs on short flight legs try to turn the aircraft as quickly as possible. You have probably heard that when Southwest was just starting out, they were short a plane and had no financing to get another. They reworked their schedule and squeezed a couple more flights out of their existing aircraft to fill the need.
Aircraft manufacturers publish an expected turn time by station. Here is one for a 737-900:

In this example, servicing galleys and boarding passengers tie for longest elapsed time. Refueling is much shorter. Maintenance does not even appear.
More important than elapsed time for any given task is time on the critical path, since many tasks can be done in parallel. In this case, boarding passengers waits for servicing cabin, which waits for deplaning passengers. LCCs typically do not serve meals, so servicing galleys could be significantly shortened. Similarly, they might use a simplified process to shorten boarding time. You might notice that the tasks that have been shortened by LCCs are on the critical path, as you would expect.

@Teodorism this is a completely separate question


text:
Out of sight planes during final approach
Does it ever happen that planes descending on a descent path (glide slope) block each other so that one (or more) plane is not visible from the tower (at the airport) or localizer? I want to know if that can cause technical issues. For example, how does a plane track a localizer if it's being blocked by the plane(s) in the front?

I think this question is too generic, the only answer to it must be "yes". So please be more specific.

@TimothyTruckle I just edited the question to make it less generic.

The localiser doesn't track the plane: the plane tracks the localiser.

@CatchAsCatchCan Thank you. I just edited the question. What if a plane blocks another plane so that the localizer stays out of sight?

The 2nd plane's pilot should notice that he is not receiving the localizer on his instruments and break off the approach.

Does this ever happen if both planes are on the same glide slope?

Not where approaches are actively controlled by ATC. Separation between planes is ensured.  At uncontrolled airports where practice approaches may be initiated by pilots on VFR days, maybe it could happen.  More commonly, something on the Gnd (like a truck, maybe a plane if it violates ground markings) blocks the localizer signal out to the planes.

Thanks. Does the blocking usually happen near landing or at the cruising altitude?

@Teodorism The ILS is only used for the last few miles of the approach to land. An aircraft at cruising altitude is either operating under ATC instruction, or on its own navigation. Either way, it doesn't care about a localiser.


text:
Is this paper's description of ATC services over the internet actually practical?
I read this paper recently; it's titled ATC over the World Wide Web,
a case study and prototypical implementation. The paper says:

"In the context of radar surveillance for regional airports DFS
  (Deutsche Flugsicherung Air Navigation Service) must provide a
  possibility for the controller to monitor and control the dedicated
  airspace in a safe manner without the need for a complex and locally
  installed radar surveillance system. In other words: The aim is to
  provide the controller in the tower with a PHOENIX Controller Working
  Position (CWP) over the World Wide Web (WWW). The CWP receives the
  surveillance data over the Internet. This approach allows the usage of
  a standard PC connected to the internet in a standardized manner (e.g.
  DSL)."

The PHOENIX is a Radar Data Processing System (RDPS) for air traffic control that's been developed at the Deutsche Flugsicherung (DFS).
My question is: why does a client need to send their ATC over the Internet for this? DFS still has to set up the hardware in the client tower. So, why doesn't the client use the conventional method to transmit/receive ATC and then, if needed, send the ATC through the Internet (on the ground) to the vendor (DFS) for real-time processing?

Unfortunately the paper is behind a paywall, so many people won't be able to read it and comment on whatever it's suggesting. You might want to investigate remote towers for more information.

Remind me not to fly during live events likely to be video streamed around the world...

“World wide web” is such a vague term that the claim does not make much sense. This leaves very strong first impression (without reading the paper itself) that it was not given much thought and therefore I wouldn't expect anything particularly clever from it.

I think what they mean is peer to peer communication.

@Teodorism, definitely not peer-to-peer. Everything on “web” is client-server and there is nothing here where anything else would make sense. I think they simply mean using common components to keep the cost down. Which is kinda obvious, not revolutionary. Depends on the level of details they discuss this—reliability is a major issue, but components like web browser and also the operating systems, are seeing frequent updates, so some testing regime for ensuring a broken update won't get pushed and cause service outage is needed.

The radar needs to be able to see the operating area. If the terrain is relatively flat you could have a radar station many miles away and still have coverage. For example, KRNT doesn't have a radar dish, it piggybacks off of KSEA (5nm isn't far, but it shows the principle).
http://open-air-data.github.io/atc-radar/ (if you zoom to the same approximate positioning as https://www.google.com/maps/@47.500892,-122.258982,27364m/data=!3m1!1e3?hl=en-US) shows the one radar station at KSEA which is also used by KBFI and KRNT (all three are in the Google Maps view if your screen is big enough).
The particular paper may be discussing using HTTP/WWW over some other data link format.

That map appears to show only long-range radar sites. Looking at several airports I know have short-range radars, I do not see them. Thought some sites (such as SATA north of San Antonio Airport) appear on the satellite view to be terminal rather than enroute radars.

For the scope of the article you should read Internet as IP VPN.In practice you would have at least dual links with some kind of SLA attached. All this is much cheaper than having and maintaining your own radar on site.  At my employer we have a system which gets information from various radars over an IP VPN ( been there , done that ).

But can't the client use the conventional system on the controller-aircraft link? Why rely on IP on that part? It won't make it cheaper to set up VPN for that part?

From the snippet posted I can infer that the article is about getting radar information to a tower controller without having to have an actual radar installed on site. The beauty of TCP/IP is that it makes the underlaying network transparent and cheap compared to previous solutions.

How can a client control a plane without a radar on site?

@Teodorism The radar needs to be able to see the operating area. If the terrain is relatively flat you could have a radar station many miles away and still have coverage. For example, KRNT doesn't have a radar dish, it piggybacks off of KSEA (5nm isn't far, but it shows the principle).

@bartonjs Thank you. This answers my question. If you post this as an answer, I'll accept it.

@bartonjs, well, from the title of the paper I suppose it is about sharing one radar installation between several airports that are just a couple of miles apart, so really the same situation as the KRNT.


text:
What are the differences between EASA (UK) and CASA flight training?
I'm a British citizen living in Australia who is tossing up on whether to train back home or in Australia. Given the sheer amount of complex information out there, I was wondering what the differences are between the PPL, CPL/ME/IR, ATPL theory & MCC/JOC training in Australia versus in the UK (or the EASA region as a whole), in terms of hour requirements, syllabus, technicalities, rules, licencing system, etc...
A comprehensive guide from those who perhaps have experience or knowledge would be great!

It might help if you can give us some idea of your goals and where you plan to fly in the long term. Just listing differences - whatever they are - may not be as helpful for you as an answer with some context.

@Pondlife: Ideally I plan to fly in Europe, due to family/homesickness, and the fact that low-hour airline jobs are more readily available, as opposed to the flight instructing, charter and bush pilot jobs that Australian low-hour pilots do. I guess two concerns are CASA to EASA conversion (should training be done in Australia), as well as Brexit - the UK's future relationship with the EASA & whether UK licences would be considered 'third country' licences, or the flexible access to pan-European airline jobs as UK citizens.

You're asking a good and interesting question, but I don't know if there's any clear answer. We can't know what Brexit will eventually mean, for example. Because this is a Q&A site, not a discussion forum, we focus on questions that have a clear, objective answer. Discussion and opinions are usually not our thing here, but perhaps a UK or AU pilots forum would have done good advice. But others may see it differently and may have good answers.

I'm an Australian PPL pilot but know some people who have gone through the UK system. Terminology differences aside, the training pathways are pretty comparable. If you choose to train in Australia you can convert your licence to the UK fairly easily by passing a flight test.
The main differences are:

In Australia you need to do 7 CPL exams and then 7 ATPL exams. Once you start each set of 7 you have 2 years to complete the remaining 6. You can self-study if you wish. In the UK there are 14 exams of each (but I think you only must do the ATPLs and CPLs are optional). You must complete all 14 within 18 months and self-study is not an option, you must attend a formal ground school.
Australia does not offer a Multi-Crew Pilot Licence, but still require a Multi-Crew Cooperation Course be completed before the ATPL.
A lot more schools in the UK are tied to an airline, greatly increasing your chances of immediate airline employment, if that is your goal. Not to say that's impossible in Australia but it only happens to a few dozen pilots per year who secure an airline cadetship.
Training in Australia will cost about $120,000 all up. In the UK seems to be about 120,000 pounds!

There are a lot more little differences but ultimately no matter where you train you will come out with an ICAO compliant licence. If you have specific questions you can either edit this one or head to chat.

Bloody hell 7 exams?  How big is each one?

@John K they vary a bit, I think the shortest is Aerodynamics which allows 75 minutes, the longest one is Flight Planning which allows 3 hours, and even that's not long enough for some. Fairly comprehensive but it beats the 14 topics the Europeans have to do...

In Canada it's one exam for the CPL, one for the instrument rating (INRAT), one for multi-crew, called IATRA, and two exams for the ATPL.

@Ben - this explanation was really useful & comprehensive in giving me a broad picture of the differences. Thank you!


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How is control of the airplane passed from one pilot to another?
In both the Tenerife accident in 1977 and the Air Florida accident in 1982, the first officer (FO) in the cockpit opposed the decision of the captain to take off. What should the FO do if the captain is determined to do the wrong - possibly even the fatal - thing?

I don't think this is a dupe.  The linked question does not address the core question here - What should the FO do if the captain is determined to do the wrong - possibly even the fatal - thing?

That's a CMR (Crew/Cockpit Resource Management) issue. Whether the core question is what the FO should do, the other question is somewhat related, while being the other way around (giving control and the other not acknowledging). Fair enough, while the Wikipedia is a good answer start, I won't do the copy/paste. Not really a duplicate IMHO, but borderline. Both questions should merge or we'll need at least 8 questions to cover most scenarios.

Another one (How are conflicts between pilot flying and pilot not-flying over aircraft control resolved?) deeply related, if not the generic case of the issue.

@Simon Well, the last sentence in the linked question seems to me to cover exactly that point, and the last sentence of the currently accepted answer seems to answer it. Of course, if the FO (or PNF) chooses not to follow the protocols and physically opposes the captain then that's a very different scenario but it's so extreme that I don't know if there's any 'standard' answer or explanation.

The linked answer is not a duplicate. The linked answer addresses the "my plane/your plane" protocols.  This question is explicitly about the "We all agree it's your plane and you're taking off without clearance!" type situation


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Airbus is to fly-by-wire as Boeing is to...?
If the control system in an Airbus is fly-by-wire, then what is the control system in Boeings? How does it work? What are its general differences from the fly-by-wire?

@JanHudec your answer comes closest but I'm not sure any of the answers there really address in enough detail what is being asked here.

Short answer: Boeing is to fly-by-wire too

Boeing uses a more direct approach to control (but both systems have warnings). In short it boils down to who has final authority of control surface actuation. Fly by wire does not just mean that control surfaces are controlled electronically (even the Cessna 172 has electric flaps) but that a computer in some way takes the pilot (or pilots) inputs and generates a control surface output. In the airbus case the computer has the final say, so if the pilot commands the plane to do something it should not, the computer will not move the control surfaces and allow it to enter such an attitude or speed. Boeing takes the reverse view and gives the pilot final authority so what ever control inputs are made translate to control surface movements.
With that in mind Boeing does have things like a yoke shaker in the event of approaching a stall and a yaw damper etc. Airbus will allow full control surface actuation with Direct Law however the plane is not normally in this mode. Boeings Standard protections and augmentations is similar but will allow the pilot to enter the conditions

"...to inform the pilot that the command being given would put the
  aircraft outside of its normal operating envelope, but the ability to
  do so is not precluded."
  (source)

On the contrary vertical stick motion in an airbus in flight actually controls load factor and not necessarily pitch directly. So its always some form of proportion to the aircrafts speed.
If memory serves Boeing control surfaces are set up such that movement of one yoke will move the other yoke in tandem, likewise they can not be simultaneously moved in opposite directions while airbus controls can be moved in opposite direction and the computer will summate the inputs (although an override button is present on each stick to disconnect the others should something be improperly acting on it).

I would argue that the 172 has electric flaps, not electronic. There's no logic, just pure electrical signal. FBW implies a flight control computer in there somewhere.

A bit of semantics, but edited to reflect.

This whole question seems to be about semantics! ;)

Using a pure definition of fly-by-wire, both Boeing and Airbus airliners can be considered fly-by-wire.
tl;dr:

Boeing has built some FBW airliners (777, 787) and some that aren't (707/720, 737, 747, 757, 767).
Airbus has built some FBW airliners (A320 series, A330, A340, A350, A380) and some that aren't (A300, A310).

long version:

Fly-by-wire (FBW) is a system that replaces the conventional manual flight controls of an aircraft with an electronic interface. The movements of flight controls are converted to electronic signals transmitted by wires [...], and flight control computers determine how to move the actuators at each control surface to provide the ordered response.
Fly-by-wire, Wikipedia

With that description in mind, both manufacturers build FBW aircraft. Pilots' control inputs are translated into aircraft flight control surface movements by a set of redundant computers.
Boeing's first FBW airliner was 1994's 777, and their only other pure-FBW design is the 787. The 748 is a partial-FBW design. Both the 777 and 787 have some computer-enforced limits in place to keep the aircraft within the flight envelope, but those limits can be overridden, and the aircraft generally are said to 'feel like a normal airplane'.
Airbus's first FBW airliner was the 1987's A320, and all their subsequent designs are FBW. Airbus's control logic is much less direct than Boeing's, containing full flight envelope protection in the 'Normal Law' configuration, and correspondingly less protection if the aircraft reverts to 'Alternate Law' mode (which is roughly comparable to Boeing FBW). None is provided in what is called 'Direct Law', where the computers simply pass commands directly to the flight control surfaces.
That said, both manufacturers build fly-by-wire airliners

Actually, Airbus' “alternate law” is nothing like Boeing's FBW. Airbus flight laws are “cooked”—you tell the computer the desired pitch- and roll-rate and the computer does it. If you release the stick, the plane will fly straight; no fiddling with trim. That applies also in alternate law, just the protections are switched off. Boeing's flight laws are “raw”—they emulate mechanical controls with trim and everything.

Boeing is to fly by wire as Airbus is to fly by computer, would probably be closer to the mark.
Both are fly by wire, but Boeing is closer to direct input - I move the yoke halfway to the limit, the controls move halfway to their limit
While Airbus is a suggestion to the aircraft as to what you'd like it to do - I move the side stick halfway to the limit, and the plane performs that action at something like half the rate the performance envelope should allow.
Sort of.

Not sort of, it's quite accurate. Boeing emulates mechanical input faithfully except it will increase resistance if you reach the flight envelope limit. While in Airbus, full forward deflection means load wings to -0.5G, full aft deflection means load wings to 2.5G, full right deflection means 25°/s roll rate right, full left deflection means 25°/s roll rate left and stick center means 1G and no roll rate. It's not a suggestion though, it's an order; the plane will do it unless it would take if beyond the flight envelope limits (but the Boeing one protects against that too).

The "sort of" was relating to the fact that Boeing isn't 100% direct input, and that Airbus has a mod which is closer to direct input, so neither system is entirely analogous to direct input, fly by wire, or fly by computer. It's about right, but can be a little fuzzy depending on the exact circumstances


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When does the airline check if an airplane can reach its destination?
It is known that - for example - LaMia Airlines Flight 2933 needed to travel 1,605 nautical miles (2,972 km), which exceeds the range of the Avro RJ85 at 1,600 nautical miles (2,963 km).
At what point in flight planning does the airline calculate and determine if an aircraft has enough fuel/range for its intended flight?

range depends on payload and fuel on board. where does the range computation appear? what data has been used for it?

There is no reliable information that it ran out of fuel.   The investigation is just beginning.  Claims that it ran out of fuel are based solely on the lack of an explosion/fireball on impact.  Someone has been watching too many Hollywood movies.

The article states that the pilots requested a hold to troubleshoot electrical problems. This tells me that fuel was not a priority at the time (unless they both didn't notice they were low on fuel). It says they asked for priority handling, but the article doesn't state the nature of the emergency. Unfortunately until the accident report comes out or transcripts are released, this is going to be pure speculation.

@KorvinStarmast, the question "when does the airline check to see if the airplane can carry enough fuel to reach its destination?" can be answered regardless of the status of LaMia 2933.

Fuel is continually monitored by the crew. They don't need a dispatcher to tell them about it, it's generally the other way around.

There is now (1 day after original post) credible information that the plane likely ran out of fuel, based on recordings of the crew's conversations with ATC.  (http://www.cnn.com/2016/11/29/americas/colombia-plane-crash-investigation/index.html)

The accident happened less than 24 hours ago, and any talk of fuel exhaustion at this stage is simply speculation.
The answer to your question is the pilots check if they have enough fuel to make the destination before every single flight. As others have said, the actual range of the aircraft is dependant on so many variables, that the quoted figure is effectively just a guideline for marketing purposes.

This doesn't at all answer the question, which is "When does the airline check if ..."

@kebs I disagree - the question specifically mentions flight planning which is completed by pilots, usually with assistance from dispatchers, who are all part of the airline, and completed before each flight.


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Do propellers generate static electricity in flight and how is that handled?
How is the risk of tribocharging (static electricity generation) by the propeller managed on an airplane? Regardless of airplane size, it seems the rotation of the propeller or engine blades could cause tribocharging somewhere in the electrical system, and that charge would have to be grounded or dissipated somehow.

While these might not be specifically for static from the prop, static dischargers help bleed charge away from the aircraft. Static definitely does build up on an airframe, requiring grounding (electrically) your plane before fueling.

I liked this answer the most, due to specifically naming the devices (static dischargers), and the reference back to my question (static on the airframe). Thank you for the helpful answer!

Near as I know it's not a big risk.  The prop is grounded to the airframe via the engine and all static charges are dissipated via static wicks or similar devices.  Grounding and electrical bonding is covered under 14 CFR §23.867 and OEM structural repair manuals.

Static charge is a minor risk compared to lightning strikes.  Static wicks help in both cases. The biggest effect of static buildup is on the ADF where it can cause erratic bearing swings. While there is some static built up from props, the biggest source is precipitation (rain) moving over the skin which is referred to as P-static.


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Where can a civilian obtain centrifuge training/testing?
Where can a civilian get high g-force training/testing in a centrifuge?  (Likely by paying.)  Preferably with and without a g-suit.  Preferably based in the US, maybe Canada.
I'm betting the US Air Force centrifuge in San Antonio, Texas, and Canada's military centrifuge in Toronto would laugh and/or hang up the phone if asked.
Crossing my fingers there's a private or educational facility that would be an option.

I sit in my chair and spin around. Sometimes I hold one of the cats while spinning, then put him down afterwards and watch him stagger diagonally across the room.

I don't have a cat.  I have a pug.  I tried this and he puked all over.  I blame you.  :-)

I am really curious to know why.  Would you share your motivations?

@TylerDurden Have you tried taping buttered toast to your cat's back & dropping him off the roof? :)

The ride at Epcot

@Simon, I'd give a kidney, and a something I probably can't mention under terms, to go back and attempt becoming a fighter pilot, if my wife could have been happy with it. (Not sure she could go through what so many brave families go through.) I'd give a kidney, but not the other part, for a flight in the back of Blue Angel #7 during a show. I'm 34 so can't start fighter pilot training. And no shot with the Angels - not a celebrity or in the media. When younger, someone told me needing contacts/glasses/surgery disqualified me. I'm happy believing they were right at the time, changing later.

Civilians can pilot/own something like an L-39C Albatros. (I doubt a F-4/F-104/F-100F/MiG-15/T-33 will be in reach for non-millionaires to own.)  Private pilot with single-engine landing/instrument rating, 1000 hours with 500 hours PIC, endorsements for high-performance/complex aircraft and high-altitude training. Then you start training on L-39C. Just beginning flight lessons. Many, many years off, but committed. I like cautiously over-doing things. Thinking centrifuge would be worth it, before someday giving it a shot with an instructor ready to take controls.  Would like to know my limit.

@andrewmh20, only gives 2.5g.  :-(  Maybe I could crank up the power...

I believe I might be able to recommend you a facility in The Netherlands. If you are interested, I'll ssl

You might be interested in www.aircombat.com.  It's probably cheaper than any centrifuge you'd find, a whole lot more fun, and still capable of giving you that dose of vitamin G.

This should be an answer, but I don't have enough points: You can get a pretty comprehensive experience at https://www.rocketcenter.com/simulator/gforceaccelerator - they operate a flight simulator, g-force accelerator, and gyroscopes

@MrMartin Interesting.  Their website says up to 3g though.  I wonder if they'd ever agree to go beyond that, but maybe theirs can't even go that high.

This is a tough one. I don't know of any civilian facilities (but it does not mean they don't exist). This is a bit of a shot in the dark but in my opinion you may want to contact NASA about the Ames Research Center 20-G centrifuge. If for no other reason than this is the only non military one that seems to exist. For what its worth high speed centrifuges are not that simple despite just being something that spins in a circle. The speeds that the unit spin at are extremely high to say the least, to do this with out ripping the whole thing apart requires careful balancing and construction so they are not exactly something you can build at home. Here is at least one company that is building them and installing them elsewhere in the world. They list a bunch of installs for other militaries that might be more open to a civilian coming in but who knows.

NASA also has a centrifuge at Goddard capable of accelerating 2.5 tons at 30 G, but iirc it is for satellites, not people.


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Why is a procedure turn required if you are more or less on the final approach course?
From this question.  I am not instrument rated.  The answers to the question explain, from the point of view of the plate instructions, if a PT is required or not.  The OP was failed for not performing a hold.
However, I can't see why a turn or hold is required at all.  If you are approaching within say 30 degrees, why would you not simply turn onto the final approach course and fly the approach (assuming that you are cleared of course)?

If you were simply cleared direct to BEJCY and cleared for the approach, then your instructor is correct and you should have completed the procedure turn as charted.

The OP was approaching from SSW from AUGIE so continuing to BEJCY puts him 21 degrees to the South.  Why not just turn right onto 007?
I am assuming no ATC instructions to do anything other than the published approach.

That question started to highlight for me why an IR rating is so damn lengthy and expensive!

As I read the referenced question, I note that the pilot was inbound from SSW (eg. lower-left of the plate).  AUGIE is SSE (lower-right of the map).  I interpret this as the pilot was using BEJCY as an IAF, not AUGIE.  So I disagree with the statement "The OP was approaching from SSW from AUGIE, so continuing to BEJCY puts him 21 degrees to the South".  We actually don't know how far off "straight-in" the course was.

Read that other question again.  He was approaching from the SSW and made an assumption based on the approach segment from AUGIE.  He wasn't actually on the AUGIE-BEJCY leg as it would be impossible to be there if he were approaching from the SSW.
His clearance was "Direct BEJCY cleared for the GPS 01 approach".  That clearance, in lieu of any specific instructions about the procedure turn, requires that the procedure turn be flown.  He assumed that because he was roughly on the extended centerline of the runway SSW of the airport that he was exempt.  However, there is no charted course there labelled "NoPT", so his assumption was incorrect.
Back to your question of why someone flying from that location would have to fly the PT, and the answer generally boils down to "TERPS".  The leg from AUGIE can be flown at 3000 ft while the area minimum safe altitude is 3100 ft.  It is very likely the minimum enroute altitude over that area is higher than 3100 feet.  This means a pilot that is using BEJCY as the IAF may be considerably higher altitude than 3000 ft.  On this approach you ideally want to be at 2500 ft by the FAF at CUCTO.  If you are approaching BEJCY from any direction other than AUGIE this means you cannot start your descent from whatever altitude you are at down to 2500' until passing BEJCY.  The procedure turn is not only for course alignment but also to descend to the procedure altitude from the enroute environment.

TL;DR - To have time to descend from the enroute altitude to the altitude for starting the approach.  ;-)

@Lnafziger Yep, that was the answer I took out of it ;).  Thanks Casey.

Thank you, that answered my question about why straight-in approaches are not ALL noPT. I have to remember to think in three dimensions.


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When flying to a towered airport when the tower is closed, what frequency should I use?
The attached picture shows the Rapid City Regional Airport, KRAP.  If I arrive after KRAP's tower is closed, which frequency should I use: 125.85 or 122.95?

You use the CTAF for announcing your position and intentions, i.e. 125.85. From the AIM 4-1-9(g):

If an airport has a tower and it is temporarily closed, or operated on
  a part-time basis and there is no FSS on the airport or the FSS is
  closed, use the CTAF to self-announce your position or intentions.

4-1-9(b) says:

The CTAF may be a UNICOM, MULTICOM, FSS, or tower frequency and is
  identified in appropriate aeronautical publications.

125.85 is marked as the CTAF on the sectional and listed in the Chart Supplement.
Note: The letter "C" in the dark circle next to the control tower ("CT") frequency indicates that the CT frequency is the CTAF frequency at that airport.

Understood, and I know the CTAF is 125.85 because the blue-circled C is next to 125.85, right?  If the blue-circled C was next to 122.95, CTAF would be that frequency?

@GarrisonNeely Yes, the C indicates the CTAF frequency. You can check the VFR chart legend for a full breakdown of all the information shown there.


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Can I obtain a license over several years?
How long does training for student, sport, recreational, or private licenses "count" toward your license, before it's considered outdated/expired?  Can you start the process, intending to spread out the expense over something like 5 years, or in that situation, do you need to "save up" and do it all within a year or two?
Bonus question - My luck that I'm just starting to look into this, and there's a private pilot ground school course starting tomorrow nearby.  Is it premature for me to take this class, not having taken any other steps?  Would it be over my head, or would I need to take it again if I don't get the private license within a certain amount of time taking the class?

Hi. When asking about licensing, regulation etc, please always state the jurisdiction you are asking about.

Sorry, United States (Michigan.)

I'm assuming you're asking about the US, since you mentioned sport/recreational licenses.
You can take as long as you like to learn to fly, although spreading it out over multiple years will actually cost more, not less. The reason is that you forget things and take a lot longer to develop the right reactions, muscle memory and feel for the aircraft. So try to fly as much as possible and do your license as quickly as possible, within whatever time and budget limits you have; I know that not everyone has the time and money to learn to fly in one month or even one year.
As for a ground school course, they're often planned to end with you taking the knowledge test required for private pilots and that test might even be included in the price. When you take the test it's valid for two years. If you don't pass your final checkride within those two years then you'll have to do the knowledge test again first. But that doesn't mean you have to do a ground school course again, you can work with an instructor and by yourself to refresh your knowledge.
But if you're not sure about how/when to start training then the best thing you can do is talk to an instructor about your situation and expectations. Any good flight school will be happy to have someone sit down with you and answer whatever questions you have. An introductory flight would be a great way to start, if you haven't already done that.

You can take as long as you want to train with the caveat that the longer you take the more money you will spend and the less progress you'll make for each hour of training undertaken.  Aside from all the minimum times, which you are sure to meet and exceed with an extended training schedule, they only time-based requirements when you take the checkride are:

A knowledge test passing certificate dated within the preceding 24 calendar months (14 CFR 61.39(a)(1)(i))
3 hours flight training with an instructor in the preceding 2 calendar months (14 CFR 61.109(a)(4) for private pilot single engine)

It would be rare to not have at least 3 hours with an instructor before your checkride to do final training and a mock checkride, so this requirement should be easily met.  As long as you take your written test when you can envision taking your practical test within the next 2 years, you are fine to take your time training.